The fortress town of Theresienstadt (Terezín in Czech), a few kilometres outside of Prague, became a Nazi ghetto-lager from 1941 to 1945. It existed with a two-fold purpose, on the one hand for confining the Jews of the Protectorate of Bohemia and Moravia and later those of the Reich, and on the other hand, in the final stages, as an instrument of propaganda directed to the international community which positively represented life and conditions of deported Jews. Within Theresienstadt many artistic and musical activities developed thanks to the presence of some of the most brilliant musicians in Europe. This book focuses on the concept of resistance and political and cultural opposition to Hitler’s regime through the musical analysis of some of the compositions created in Theresienstadt. In particular the two composers taken into consideration are Viktor Ullmann and Gideon Klein. The Sonata by Gideon Klein and the Sonata n. 5 and n. 6 by Viktor Ullmann, composed in 1943, are analysed in this book. The last chapter of the book focuses on the opera The Emperor of Atlantis or Death Abdicates written by Ullmann between 1943 and 1944, a work which recalls other compositions through frequently occurring musical fragments to effect a strong political and spiritual message. This book investigates the meaning of the aesthetic choices of the two composers to better comprehend the philosophical thought and message of political and cultural resistance.